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OCR A Level Chemistry A – Module 3 Periodic Table and Energy

3.2.3
Chemical
Equilibrium

Section 3.2.3 covers dynamic equilibrium in a closed system, le Chatelier’s principle for temperature, pressure and concentration, why a catalyst leaves the position of equilibrium unchanged, the techniques used to investigate equilibria, the industrial compromise between equilibrium and rate, and the equilibrium constant Kc: expressions, calculations from equilibrium concentrations and estimating the position of equilibrium from its size.

Exam Paper
Paper 1 & 3
H432/01 and H432/03
Specification Points
3.2.3 (a) – (g)
7 learning outcomes
Topic Parts
4 pages
Revision notes available
Exam Board
OCR A
H432 (2015 onwards)

Revision Notes

Work through 3.2.3 Chemical Equilibrium in a structured sequence.

Reversible
Dynamic
Equilibrium
1
Available

Dynamic Equilibrium

Dynamic equilibrium: reversible reactions, equal forward and reverse rates, constant concentrations, closed systems and the position of equilibrium.

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Shifts
Le Chatelier’s
Principle
2
Available

Le Chatelier’s Principle

Le Chatelier’s principle: temperature, pressure and concentration changes, catalysts, and the ammonia and chromate equilibria as examples.

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Yield versus rate
Equilibria in
Industry
3
Available

Equilibria in Industry

Equilibria in industry: the Haber and Contact processes, compromise temperature and pressure, catalysts and evaluating yield data.

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Products over reactants
Equilibrium
Constant Kc
4
Available

The Equilibrium Constant Kc

Kc: expressions, units, calculations from equilibrium amounts, the magnitude of Kc and the effect of temperature.

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Specification Coverage

3.2.3 Chemical Equilibrium – OCR A Level Chemistry A

The following OCR A learning outcomes state what candidates should be able to do. Wording is taken from the OCR A Level Chemistry A (H432) specification.

3.2.3 Chemical equilibrium

3.2.3(a)
explanation that a dynamic equilibrium exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and the concentrations of reactants and products do not change
3.2.3(b)
le Chatelier’s principle and its application, for homogeneous equilibria, to deduce qualitatively the effect of a change in temperature, pressure or concentration on the position of equilibrium
3.2.3(c)
explanation that a catalyst increases the rate of both forward and reverse reactions in an equilibrium by the same amount, resulting in an unchanged position of equilibrium
3.2.3(d)
the techniques and procedures used to investigate changes to the position of equilibrium for changes in concentration and temperature
3.2.3(e)
explanation of the importance to the chemical industry of a compromise between chemical equilibrium and reaction rate in deciding the operational conditions
3.2.3(f)
expressions for the equilibrium constant, Kc, for homogeneous reactions and calculations of Kc from provided equilibrium concentrations
3.2.3(g)
estimation of the position of equilibrium from the magnitude of Kc